Hello,
Can you please check the vehicle's attitude (roll, pitch, yaw) when it is sitting flat, right before take-off? You can look at PX4 logs or live using GCS.
If the IMU is not calibrated properly, and the vehicle thinks that it is tilted, it will try to compensate for it by tilting in opposite direction, so it can appear as if one of the motors is not able to spin faster, when in fact the flight controller could be commanding it to spin slowly. This is just one reason why this could be happening, so it is worth checking.